There are a variety of different terms you may come across in relation to online video.
Streaming Video – Any video that does not require you to download a video file before viewing it. The video is delivered to you ‘live’, similar to a live television broadcast, and the video is not stored permanently on your computer.
File-based video – Video where you download a file first, then watch it. The file stays on your computer, unless you delete it. Video files are generally quite large in size, much larger than music files or word documents for instance. This is why they typically take longer to download.
Windows Media Player, Real Player, Quicktime – The 3 most popular types of ‘player software’ for watching video on your computer. You will need at least one of these programs to be able to watch video on your computer, some people install all 3. Luckily they are free to download, and in most cases at least one of them will already be installed on your system. While the lines between the 3 are blurring in terms of compatibility with each other, when it comes to streaming video (as opposed to file-based video), the three systems are essentially incompatible. If a live Internet broadcast is only available in Windows Media format, you will need to have Windows Media Player installed. Same for Quicktime, same for Real Player.
Real Player has gradually become a ‘non’ player due to its increasingly bloated software, upsell demands, and annoying interface, although it was the first to introduce the concept of streaming in 1995. Some people these days prefer a new community-built player called VLC, that aims to be compatible with all formats, except Real that is. I don’t recommend it for average users, far easier to stick with the branded players. Avoid installing Real Player unless you absolutely have to. It’s just too bloated. An alternative for PC users is a program called appropriately Real Alternative.
Compression – A system whereby information such as a video file can be compressed into a smaller file, usually with a slight loss in quality. The idea is that the smaller file will be quicker to download. Photo files that have a .jpg extension are an example of a file that has been compressed. MP3 audio files are another example.
DIVX – A type of compression system that has became particularly popular among people who illegally copy DVD’s, and then make them available as ‘DIVX files’ for downloading on the Internet. Note that the common media players will not play DIVX files without installing the separate DIVX software. In technical terms you are installing a DIVX codec, that enables your media player to decompress (and thus play) the DIVX file.
Peer to Peer (P2P) – A concept whereby large files such as video can be exchanged among users in a decentralized fashion. You are downloading a file from someone else’s computer, and people are downloading files from your computer. There is no central repositry of files. Think of it like a library where everyone has copies of the books, and you exchange books directly with other users.
The first program of this kind was Napster, more recent examples are Kazaa, Limewire and Morpheus. These programs are generally used to distribute illegal files, and the companies behind them frequently get shut down. For this reason, and because these systems are frequently used for distributing viruses, P2P has gotten a bad name, although it offers many advantages to traditional means of electronic distriibution.
Note that these days many P2P programs can access the files of other P2P software.
Bittorrent – A newer type of Peer-to-Peer software, somewhat more complicated to understand and use. It is an open source system meaning there are many different people providing alternative pieces of software for accessing it. As such, no single person or company can be identified to shut it down, and there are many completely legal users of the system. For this reason it is likely to be around for a while, and gradually (inexorably) it is getting easier to use.
Torrent – A small file that points to a larger file in the Bittorrent system. Typically you would click a link on a website to a torrent file, which then tells your Bittorrent software to go grab the much larger file you want.
eDonkey (also called ed2k) – Yet another peer-to-peer system, particularly popular for distributing video files. Easier to use than bittorrent, but now the company behind it has washed its hands of it. Enthusiasts and its large base of users keep it going.
DRM – Digital Rights Management. Any system that controls who can open a file, or how it is used. Primarily used for restricting access to paid content.
IPTV – Internet Protocol Television. Systems for delivering television over broadband connections in a similar way to cable or satellite. This generally refers to a closed system, where a set-top box plugs into your broadband connection, and provides a video signal for viewing on your normal television.
VOD – Video on Demand. A catch-all phrase for any system that allows you to view video when you want. Can be offered via IPTV, cable TV and Internet TV.
RSS – A system allowing you to be notified when content on a particular website changes.
P2PTV – Peer to Peer Television. This is the same idea as P2P file sharing, only instead of a group of people sharing files, they are sharing live television streams. A number of programs for doing this exist, with most of them coming out of China, due to the demand among ex-pat Chinese to see television from their home country.
The programs rely on a few people on the network connecting their computers to their TV signal, although often the makers of the software themselves provide this service. These programs are typically illegal, since the P2P nature of the programs mean that the television signals are being rebroadcast publicly to many users. This is not allowed under the terms and conditions of the vast majority of television broadcasters, and copyright laws in general.
I will update these definitions over time, so feel free to link to or bookmark this page.